The present invention relates to an exhaust apparatus of an outboard motor.
In known art, Japanese Patent Laid-open Publication No. HEI 6-129224 discloses one example of an exhaust apparatus of an outboard motor in which an exhaust passage connected to an exhaust port of a cylinder head is integrally formed in a cylinder block, and Japanese Utility Model Laid-open Publication No. HEI 4-134626 also discloses an exhaust apparatus of an outboard motor in which a separate exhaust manifold is disposed between a cylinder head and an oil pan which is formed with an exhaust passage.
However, in the known art mentioned above, in the exhaust apparatus in which the exhaust passage is integrally formed in the cylinder block, the cylinder block is increased in size and in weight, and its shape is complicated, which increases manufacturing costs. Further, since the exhaust passage is formed in the vicinity of the cylinder, the exhaust heat may thermally deform the cylinder, which is not preferable. Furthermore, since the cylinder and the exhaust apparatus commonly use the same cooling water jacket, it is impossible to adjust the temperature of only the exhaust apparatus.
In order to eliminate the above defects in the prior art, it may be possible to use a separate exhaust manifold. However, since an exhaust port is normally disposed at a location close to a rear portion of the engine, if the exhaust manifold is connected to the exhaust port, a width of the engine is increased, being disadvantageous in terms of layout, and moreover, a shape of an engine cover having stream line (substantially elliptic shape) section may be deformed.